Podcast
Questions and Answers
What is the primary purpose of decision structures in programming?
What is the primary purpose of decision structures in programming?
- To declare functions within a program.
- To allow a program to execute different instruction sequences based on certain conditions. (correct)
- To define the data types used in a program.
- To repeat a block of code multiple times.
In Python, which statement is used to implement a simple decision structure?
In Python, which statement is used to implement a simple decision structure?
- `while`
- `for`
- `def`
- `if` (correct)
What does the term 'two-way decision' refer to in programming?
What does the term 'two-way decision' refer to in programming?
- A decision structure that evaluates two different conditions simultaneously.
- A decision structure where the program chooses between two alternative code paths. (correct)
- A decision that requires input from two different users.
- A decision made by comparing two different variables.
In Python, how is a two-way decision typically implemented?
In Python, how is a two-way decision typically implemented?
What programming construct is used to handle multiple mutually exclusive outcomes?
What programming construct is used to handle multiple mutually exclusive outcomes?
What is the purpose of exception handling in programming?
What is the purpose of exception handling in programming?
What is a Boolean expression?
What is a Boolean expression?
What is the bool data type used for?
What is the bool data type used for?
What does 'lexicographic' ordering refer to when comparing strings?
What does 'lexicographic' ordering refer to when comparing strings?
If you have the following code, if x > 5: print("Greater"), what happens if x is equal to 5?
If you have the following code, if x > 5: print("Greater"), what happens if x is equal to 5?
What is a common mistake when writing conditional statements in Python?
What is a common mistake when writing conditional statements in Python?
Consider the code: if temperature > 90: print("Heat warning"). What type of decision structure is this?
Consider the code: if temperature > 90: print("Heat warning"). What type of decision structure is this?
In Python, how do you indicate that a set of statements belongs to the body of an if statement?
In Python, how do you indicate that a set of statements belongs to the body of an if statement?
What happens if the condition in an if statement is False?
What happens if the condition in an if statement is False?
In the context of the quadratic equation solver, what is the discriminant used for?
In the context of the quadratic equation solver, what is the discriminant used for?
What happens if the discriminant of a quadratic equation is negative?
What happens if the discriminant of a quadratic equation is negative?
What is nesting in the context of if-else statements?
What is nesting in the context of if-else statements?
Why is the elif statement used in Python?
Why is the elif statement used in Python?
Which of the following represents the correct syntax for a multi-way decision in Python?
Which of the following represents the correct syntax for a multi-way decision in Python?
In a multi-way if-elif-else statement, when is the else block executed?
In a multi-way if-elif-else statement, when is the else block executed?
In finding the maximum of three numbers using the 'compare each to all' strategy, what logical operator is essential?
In finding the maximum of three numbers using the 'compare each to all' strategy, what logical operator is essential?
When determining the largest of three numbers (x1, x2, x3) using the decision tree strategy, what is the maximum number of comparisons required?
When determining the largest of three numbers (x1, x2, x3) using the decision tree strategy, what is the maximum number of comparisons required?
In the sequential processing strategy for finding the maximum value in a series, what action is taken when a larger value is found?
In the sequential processing strategy for finding the maximum value in a series, what action is taken when a larger value is found?
What is a potential drawback of the decision tree strategy for finding the maximum of several values, compared to the 'compare each to all' strategy?
What is a potential drawback of the decision tree strategy for finding the maximum of several values, compared to the 'compare each to all' strategy?
Which of the following is an advantage of using Python's built-in max() function to find the largest number?
Which of the following is an advantage of using Python's built-in max() function to find the largest number?
What is the most direct translation of “x is not equal to y”?
What is the most direct translation of “x is not equal to y”?
Consider this code snippet: if score >= 90: grade = 'A' elif score >= 80: grade = 'B'. What will the value of grade be if score is 85?
Consider this code snippet: if score >= 90: grade = 'A' elif score >= 80: grade = 'B'. What will the value of grade be if score is 85?
What is the meaning of the keyword 'in' in Python?
What is the meaning of the keyword 'in' in Python?
If you expect the execution in one and only one branch of code, which approach will you use?
If you expect the execution in one and only one branch of code, which approach will you use?
x = 10
y = 5
if x > y:
result = 'x is greater'
else:
result = 'y is greater or equal'
print(result)
What will this code output?
x = 10
y = 5
if x > y:
result = 'x is greater'
else:
result = 'y is greater or equal'
print(result)
What will this code output?
What happens when an exception is raised within a try block?
What happens when an exception is raised within a try block?
What is the advantage of using exception handling over simply letting a program crash when an error occurs?
What is the advantage of using exception handling over simply letting a program crash when an error occurs?
In Python, which operator is used to test for equality?
In Python, which operator is used to test for equality?
In Python, can you directly chain comparison operators like this: if 1 < x < 5?
In Python, can you directly chain comparison operators like this: if 1 < x < 5?
age = 20
status = 'minor' if age < 18 else 'adult'
print(status)
What value will be printed in 'status'?
age = 20
status = 'minor' if age < 18 else 'adult'
print(status)
What value will be printed in 'status'?
What is the main difference between an if statement and a while loop in Python?
What is the main difference between an if statement and a while loop in Python?
Which of the following data types can be used as a condition in an if statement?
Which of the following data types can be used as a condition in an if statement?
x = 5
if x > 10 :
print("A")
elif x > 5:
print("B")
else:
print("C")
What will be printed?
x = 5
if x > 10 :
print("A")
elif x > 5:
print("B")
else:
print("C")
What will be printed?
Which of comparison operators can be used to compare two strings in Python to find out if one string is lexicographically greater than the other?
Which of comparison operators can be used to compare two strings in Python to find out if one string is lexicographically greater than the other?
What will be printed if you run this code? ```python
value = -5
if value > 0:
print('Positive')
elif value == 0:
print('Zero')
else:
print('Negative')
What will be printed if you run this code? ```python value = -5 if value > 0: print('Positive') elif value == 0: print('Zero') else: print('Negative')
Flashcards
What are decision structures?
What are decision structures?
Statements that allow a program to execute different sequences of instructions for different cases.
Simple Decision
Simple Decision
A programming pattern where a decision leads to one possible action.
Control Structure
Control Structure
Alters the sequential program flow.
Python if statement
Python if statement
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Simple Conditions
Simple Conditions
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Boolean data type (bool)
Boolean data type (bool)
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Lexigraphic Ordering
Lexigraphic Ordering
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Two-way Decision
Two-way Decision
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if-else statement
if-else statement
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elif
elif
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if-elif-else
if-elif-else
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Nesting
Nesting
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max() function
max() function
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Study Notes
- Python's
ifstatement is used to implement decision structures in programs. - Control structures are what makes it possible to alter sequential program.
- Decision structures are statements that allow a program to execute different sequences of instructions based on different cases.
- Using decision structures, programs can "choose" an appropriate course of action.
Objectives for using decision structures and if statements in Python include:
- Implementing simple decisions using the Python
ifstatement. - Implementing two-way decisions using the Python
if-elsestatement. - Implementing multi-way decisions using the Python
if-elif-elsestatement. - Recognizing exception handling and writing simple exception handling code for standard Python run-time errors.
- Using Boolean expressions and the
booldata type effectively. - Reading, writing, and implementing algorithms with decision structures, including sequences and nested structures.
Temperature Warnings Program Example
- The goal is to modify a Celsius to Fahrenheit conversion program to print a warning for extreme temperatures.
- Temperatures over 90 degrees Fahrenheit trigger a "heat warning".
- Temperatures below 30 degrees Fahrenheit trigger a "cold warning".
- The algorithm involves inputting the temperature in Celsius, converting it to Fahrenheit, outputting the Fahrenheit temperature, and then checking if a heat or cold warning needs to be issued.
- Indentation is used to signify what should be executed if the condition is true.
- The Python
ifstatement implements the decision-making process in the program. if <condition>:followed by the indented<body>of statements.- First, the condition in the heading is evaluated.
- Second, If the condition is true, the sequence of statements in the body is executed, and then control passes to the next statement in the program.
- Else, the statements in the body are skipped, and control passes to the next statement in the program.
- The
ifstatement makes a one-way or simple decision in Python.
Forming Simple Conditions
- Conditions involve simple comparisons.
- The format is
<expr> <relop> <expr>. relopmeans relational operator.==is used for equality checks because=is used for assignment.- Using
=in conditions is a common mistake. - Conditions can compare numbers or strings.
- String comparisons are lexigraphic, sorting strings based on their Unicode values such that uppercase letters come before lowercase.
- Boolean expressions are named after mathematician George Boole.
- Boolean expressions evaluate to
true(if the condition holds) orfalse(if it does not hold). - Some languages use
1and0to represent"true"and"false". - Boolean conditions are data type
bool. TrueandFalseare literals that represent Boolean values.
Two-Way Decisions
- When b²-4ac < 0, quadratic equation programs crash because they cannot compute the square root of a negative discriminant.
- Checking for this situation is possible through an
ifstatement to avoid program crashes. - One approach is to calculate the discriminant and include an
ifstatement to proceed only if the discriminant is non-negative. - The Python
if-elsestatement is a two-way decision structure. if <condition>:followed by theelseifandelsestatements.- When Python finds this structure, it evaluates the condition.
- If true, Python executs the statements under the
if. - If false, Python executes the statements under the
else. - Subsequently, Python executes any statements following the
if-elseblock.
Multi-Way Decisions
- Multi-way decisions are used to handle more than two possible outcomes.
- You can check the value of discrim when less than 0, greater than 0, or equal to 0 to handle all root possibilites.
- Nesting can creates a compound statement inside another.
- The
elifstatement combines anelseimmediately followed by anif. elifprovides a concise way to handle multiple conditions.- The format for multi-way decisions with
elifstatements if <condition1>:followed by conditional code block.elif <condition2>:followed by conditional code block.else:followed by code block.- Python evaluates each condition in turn until it finds one that is true then executes its associated statements.
- Control passes to the next statement after the entire
if-elif-elseblock, andelseis optional
Finding the Max of Three Numbers
- Three ways to do this:
- compare each to all
- decision tree
- sequential processing
- Given the
main()function framework, the goal is to find missing code that setsmaxto the largest of three numbers. - Need an algorithm to find the largest of three values (x1, x2, x3).
Strategy 1: Compare Each to All
- Each number is compared to the others to determine which one is the largest.
if x1 >= x2 and x1 >= x3: maxval = x1- This is syntactically correct in Python.
- Four boolean expressions are needed when finding the max of five values.
Strategy 2: Decision Tree
- An if-else nested 3 levels deep is more efficient
- With this method two comparisons occur no matter what.
Strategy 3: Sequential Processing
- Start by scanning through a list for a large number, and mark it. Then find the largest number and use that.
- This idea can be translated into Python easily.
- A program that prompts a user for a number, then compares to a max value, allowing the user to do this multiple times.
Strategy 4: Use Python
- The code
print("The largest value is", max(x1, x2, x3))to efficiently find the max. - Python has a built-in funciton `max that returns the largest of its parameters.
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